This invention relates to fusing toner images and more particularly to a device used for fusing toner images.
The invention can be utilized in the art of xerography or in the printing arts. In the practice of conventional xerography, it is the general procedure to form electrostatic latent images on a xerographic surface by first uniformly charging a photoreceptor. The photoreceptor comprises a charge retentive surface. The charge is selectively dissipated in accordance with a pattern of activating radiation corresponding to original images. The selective dissipation of the charge leaves a latent charge pattern on the imaging surface corresponding to the areas not exposed by radiation.
After the electrostatic latent image is recorded on the photoconductive surface, it is developed by bringing a developer material into contact therewith to thereby form toner images on the photoconductive surface. The images are generally transferred to a support surface such as plain paper to which it may be permanently affixed by heating or by the application of pressure or a combination of both.
One approach to thermal fusing of toner material images onto the supporting substrate has been to pass the substrate with the unfused toner images thereon between a pair of opposed roller members at least one of which is internally heated. During operation of a fusing system of this type, the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the heated fuser roll to thereby effect heating of the toner images within the nip.
Fuser rolls are typically made from a tube of high thermal conductivity metal with end hubs or caps pressed and pinned or brazed or spin welded to the ends of the roll. The primary function of the hub, in particular a journal portion thereof, is to allow the bearing to be attached to a reasonably small diameter. The secondary function is to reduce heat flow out of the end of the roll. This will keep the bearing temperature low thereby increasing the the life of the grease and the bearing, and it will promote a more uniform temperature along the length of the roll near the roll ends.
Glass reinforced polyamide hubs used for some rolls were found to be unacceptable due to a finite fatigue life and being very fragile. Also, this type of end cap does not lend itself to spin welding.
Stainless steel has been used because of its relatively low thermal conductivity but it is very expensive. It does have reasonable reclaim life but galls sooner than desired.
Aluminum has been used due to its low cost. Fuser core reclaim is not feasible with these hubs as they have exhibited galling when used as a journal. Also, aluminum end caps are very thermally conductive.
Following is a discussion of prior art, incorporated herein by reference, which may bear on the patentability of the present invention. In addition to possibly having some relevance to the question of patentability, these references, together with the detailed description to follow, may provide a better understanding and appreciation of the present invention. These patents disclose instances where the physical properties of ceramic materials are exploited for various purposes relating to development and fusing of electrostatic latent images.
U.S. Pat. No. 5,191,381 granted to Jie Yuan on Mar. 2, 1993 discloses a ceramic heat roller whose body is formed of a resistor material having a positive coefficient of resistance (PTC) capable of self-heating and self-regulating temperature.
U.S. Pat. No. 4,109,135 granted to Minden et al on Aug. 22, 1978 discloses a fuser roll assembly for fusing xerographic materials. The fuser assembly comprises end caps which, as stated in the specification thereof, are preferably constructed of a poor heat conductor, such as stainless steel or an appropriate plastic or ceramic, for example.
U.S. Pat. No. 5,298,957 granted to Haupt et al on Mar. 29, 1994 discloses a way of reducing wear on the ends of a fuser roll and the fuser bearings due to the thermal expansion of the user roll. To this end, a fuser roll collar is provided with plurality of protrusions on its outer surface such that they contact the inner surface of a bearing to minimize heat transfer between the fuser roll collar and the fuser bearing.
U.S. Pat. No. 4,544,828 discloses a heating device utilizing ceramic particles as a heat source and adapted for use as a fixing apparatus. This patent also discloses anti-abrasive sleeves disposed intermediate a bearing and a fuser roll shaft.
U.S. Pat. No. 4,893,151 discloses a single component image developing apparatus including a developing roller coated with a Chemical Vapor Deposition ceramic and an elastic blade coated with a ceramic.
U.S. Pat. No. 5,043,768 discloses a rotating release liquid applying device for a fuser including an outer porous ceramic material.